Method and apparatus for preventing loss of uplink data in wireless communication system

1. A method performed by a central unit (CU) of an integrated access and backhaul (IAB)-donor in a wireless communication system, the method comprising:

receiving, from a wireless device, uplink data through a source IAB-node;

receiving, from the source IAB-node, a message which informs that uplink packets among the uplink data are remained on the source IAB-node, wherein the message is related to handover procedures of the wireless device from the source IAB-node to a target IAB-node; and

proceeding the handover procedures, after receiving the uplink packets.

2. The method of claim 1 , wherein the method further comprises,

waiting for the handover procedures, until receiving all of the uplink packets.

3. The method of claim 1 , wherein the method further comprises,

determining that all of the uplink packets are received based on the message.

4. The method of claim 1 , wherein the handover procedures includes transmitting a SN Status Transfer message to a CU of other IAB-donor, wherein the other IAB-donor is connected with the target IAB-node.

5. The method of claim 4 , wherein the method further comprises,

forwarding the uplink packets to the CU of the other IAB-donor.

6. The method of claim 4 , wherein the SN Status Transfer message includes a PDCP Sequence Number (SN) and/or a Hyper Frame Number (HFN).

7. The method of claim 1 , wherein the handover procedures includes performing a UE Context Release procedure to a distributed unit (DU) of the source IAB-node, wherein the source IAB-node is connected with the DU of the IAB-donor and the target IAB-node is connected with other DU of the IAB-donor.

8. The method of claim 1 , wherein the message includes a No UL Data Indication informing that no uplink packets among the uplink data is remained on the source IAB-node.

9. The method of claim 8 , wherein the handover procedures is proceeded, when the received message includes the No UL Data Indication.

10. The method of claim 1 , wherein the wireless device is an UE or another IAB-node.

11. The method of claim 1 , wherein the message is a Downlink Data Delivery Status or a new message using F1 user plane interface (Fl-U).

12. The method of claim 1 , wherein the message is an UE Context Modification Response message using F1 control plane interface (F1-C).

13. The method of claim 1 , wherein the message includes UE ID, Bearer ID, PDCP sequence number of transmitted uplink packets, PDCP sequence number of uplink packets to be transmitted, RLC sequence number assigned by the UE/the IAB-node DU for transmitted uplink packets, and/or RLC sequence number assigned by the UE/the IAB-node DU for uplink packets to be transmitted.

14. The method of claim 1 , wherein the wireless device is an autonomous driving apparatus in communication with at least one of a mobile terminal, a network, and/or autonomous vehicles other than the wireless device.

15. An integrated access and backhaul (IAB)-donor in a wireless communication system, the IAB-donor comprising:

a distributed unit (DU) of the IAB-donor; and

a central unit (CU) of the IAB-donor, operably coupled to the DU of the IAB-donor, and configured to:

receive, from a wireless device, uplink data through a source IAB-node and the DU of the IAB-donor;

receive, from the source IAB-node, a message which informs that uplink packets among the uplink data are remained on the source IAB-node, wherein the message is related to handover procedures of the wireless device from the source IAB-node to a target IAB-node; and

proceed the handover procedures, after receiving the uplink packets.